Support go1.10

Add stubs for the new testDeps interface functions. Also removes testing
for 1.8.

Change-Id: Ice58cca20658d905df9fb87e822d7861abf60976
diff --git a/context.go b/context.go
index ebe4e12..f131024 100644
--- a/context.go
+++ b/context.go
@@ -1097,7 +1097,7 @@
 				Pos: assignment.EqualsPos,
 			}
 		default:
-			panic(fmt.Errorf("unknown value type: %d", assignment.Value.Type))
+			panic(fmt.Errorf("unknown value type: %d", assignment.Value.Type()))
 		}
 	}
 }
@@ -1115,7 +1115,7 @@
 				Pos: assignment.EqualsPos,
 			}
 		default:
-			panic(fmt.Errorf("unknown value type: %d", assignment.Value.Type))
+			panic(fmt.Errorf("unknown value type: %d", assignment.Value.Type()))
 		}
 	}
 }